The instant invention is related to a method for making microemulsions. More particularly the instant invention is related to a method of making microemulsions having an average particle size of from about 0.001 microns to about 0.05 microns.
Microemulsions containing silicone fluids have been found to be useful in a variety of personal care products such as hair conditioners and other cosmetic formulations. As defined herein, the term "microemulsions" refers to transparent, mechanically and thermally stable systems comprising small droplets having a mean or average particle diameter usually not more than 0.05 microns in diameter, preferably not more than 0.040 microns in diameter and most preferably not more than 0.025 microns in diameter. The small size of the droplets imparts a high degree of transparency to the emulsion. Cosmetic formulations containing microemulsions possess improved aesthetic values as well as improved physical properties.
The use of microemulsions in cosmetic applications is known in the art, see for example U.S. Pat. Nos. 4,797,272 (Linnet al.) and 4,620,878 (Gee). U.S. Pat. No. 4,797,272 to Linnet al. discloses water-in-oil microemulsion compositions having a mean droplet size ranging from about 0.001 microns to about 0.200 microns and containing moisturizers or sunscreens, surfactants, oils (e.g. cyclic dimethyl polysiloxanes), and skin humectants. U.S. Pat. No. 4,620,878 to Gee discloses a polyorganosiloxane emulsion that contains a polyorganosiloxane containing at least one polar radical such as an amino radical attached to the silicon of the siloxane by Si--s C or Si--O--C bonds or at least one silanol radical and a surfactant that is insoluble in the polyorganosiloxane. The emulsion prepared by Gee has an average particle size of less than 0.14 microns and can be prepared by forming a translucent oil concentrate by mixing the polyorganosiloxane, at least one surfactant, an water and then forming a polyorganosiloxane emulsion of the oil-in-water type by rapidly dispersing the translucent oil concentrate in water.
It continues to be desirable to provide alternative or improved methods for preparing microemulsions of small average particle size. The instant invention arises from the discovery that the average particle size of silicone microemulsions can be reduced by preparing silicone microemulsions using the techniques of emulsion polymerization. This discovery may be broadened to include other microemulsions achievable by emulsion polymerization, such as the formation of aqueous microemulsions of polyacrylates or latexes.